A radio frequency identification device (“RFID”) by definition is an automatic identification and data capture system comprising readers and tags. Data is transferred using electric fields or modulated inductive or radiating electromagnetic carriers. RFID devices are becoming more prevalent in such configurations as, for example, smart cards, smart labels, security badges, and live stock tags.
Typically, a smart card is a flexible, credit card size, plastic device embedded with a chip that provides memory, microprocessing capability, and RF transmission and reception (a “transceiver”). When employed with a “reader,” operating power is supplied to the chip and the reader communicates with the chip to read and, in some applications, write information to the chip. As is well known, all of these integrated circuit devices, or “chips,” are manufactured in mass quantities on silicon “wafers.” The wafers are cut into multiple “die,” each of which is a discrete, individual chip. Many of these terms (e.g., die, chip, microprocessor) are used interchangeably in the art. In this application, the term “chip” is used hereinafter to refer to any form of discrete or integrated circuit device, either active or passive, and electro-optic devices.
In their initial applications conventional smart cards (sometimes known as “chip cards”) contained a “chip module” embedded in a credit card sized piece of plastic. A chip module is a chip that is “packaged” with, or pre-connected to, a substrate (a “chip carrier”), usually prepared with contact areas and conducting tracks, to allow for easier handling and connection of the chip within a circuit assembly. The cards could be “read” by being plugged into a reader so that pins in the reader physically touched a “contact plate,” i.e., an exposed contact area of the chip module. The contact plate contained a number of conductors that communicated with the reader via the pins. These “contact” smart cards were more versatile than “swipe” cards, which contain a limited amount of information, such as, a customer account number, in a magnetic strip on one side of the card. On the other hand, these early smart cards were still limited by the need to physically contact or insert the card into a reader, thereby slowing down the speed with which transactions could be completed.
Several things have greatly expanded the potential applications for smart cards. Among these is the continued development of processing capability and memory storage capacity associated with ever smaller chips. This has enabled smart cards to be employed in new ways that require larger amounts of data storage or processing capability. In addition, new “contactless” smart cards have been developed that do not require physical contact of the smart card with the reader. These contactless smart cards employ technology similar to that of RFID cards, which have been used for a number of years in security or access control situations. These RFID cards are usually hard, rigid, flat devices that contain a chip and an antenna. The RFID cards are powered by radio frequency (“RF”) energy generated by a reader that energizes a circuit within the RFID card and enables the exchange of a limited amount of information between the RF reader and the chip in the card.
Typically, the new contactless smart cards are the same size as a credit card and work like an RFID card. However, the ability of a smart card to store vast amounts of information with great security has spurred its use in a number of applications. Smart cards were initially employed commercially as “phone cards,” storing a prepaid dollar amount in memory for authorizing telephone usage, particularly at public telephones. Communications between the telephone and the card authorize or deny usage of the telephone and deduct the amount of the telephone charges from the available amount maintained in memory. Smart cards are now employed as electronic debit/credit cards, as “loyalty” cards, and for accessing and utilizing pay-television and mass transit facilities. They are also being deployed as electronic tickets for exhibitions and events, for the storage of and ready access to individual health/medical records, and for vehicle anti-theft systems. New uses are being created regularly.
The transfer of information by RF has expanded the possible applications for smart cards by eliminating the need for physical contact of a contact plate of a smart card with a reader. The addition of a miniature antenna (for example, a coil or dipole) in the card body enables the contactless card to communicate via RF waves, thereby permitting a greater range of operation, e.g., about one meter utilizing current commercial technology. Further technological improvements are expected to significantly increase the operating range of these contactless smart cards. Eliminating the need for contact between the smart card and the reader reduces the time that it takes the reader to access and communicate with the smart card, making smart cards more acceptable to users. Improved reader accessibility to the cards reduces queuing time, making smart cards much more user friendly, for example, in situations where numerous people need to pass rapidly through a limited number of access points (e.g., gates to mass transit systems and event facilities).
Another new development is a hybrid, or “dual-interface,” smart card that contains both a contact plate and an antenna and can be energized and accessed by either a contact reader or RF reader. Both interface capabilities are therefore resident in a single smart card. Unless otherwise indicated, as used hereinafter, the term “smart card” encompasses traditional smart cards, contactless smart cards, and dual-interface smart cards.
Generally, smart cards are utilized by individuals and retained and secured by them, for example in a wallet or purse, in the same manner as a credit card. Alternatively, a smart card may be worn by the user like an identification badge. Smart cards may also be employed as a “tag” to monitor, for example, the movement of books, clothing, or other retail products, or even livestock or wild animals.
Technological improvements have enabled RFID devices to be employed in increasingly smaller and thinner forms, for example, as labels on inanimate objects or for verification of legal documents. These small, thin, flexible RFID components are hereinafter termed “smart inlays.” Smart inlays are typically the size of a postage stamp and generally comprise a programmable integrated circuit chip connected to an antenna on a substrate. Although a smart inlay might be read by contact with a scanner, its primary purpose is to provide a label containing information which can be transferred without the need for time-consuming, individualized scanning, for example, optical scanning of one- or two-dimensional bar codes.
One form of use for a smart inlay is in a “smart label.” Smart labels typically comprise a thin laminate of paper or plastic enveloping a smart inlay, which enables communication through RF signals over considerable distances, e.g., one meter or more. Accordingly, smart labels attached, for example, to overnight courier packages or airline baggage, or used as retail labels, or for rental services (e.g., library books and videos). Smart labels need not be individually manipulated relative to a scanner, but may transfer information in the normal course of handling the package, for example, while placing the package on a conveyor or loading the package onto a cart or truck as the package passes a fixed reader. In addition, and unlike a bar coded label with fixed information, the data stored in the chip memory of the smart label can be modified by transmitting updated data from a reader without the need to replace the label. The paper or plastic laminate of the smart label containing the smart inlay may be printed with identification, or even corresponding optical bar codes, similar to regular packaging labels.
Another form of smart inlay use is in the creation of “smart paper.” Smart paper is a paper document that contains a smart inlay, usually for authenticity or verification purposes—like an electronic watermark. Examples of documents that may use a smart label are personal identification, stock certificates, bonds, wills, and other legal documents where proof of authenticity is desirable.
In typical uses, smart inlays are also inductively powered by the RF field emanating from the reader and do not need a battery. Because smart cards and smart inlays are powered electrically by the reader, they may be classified, in one sense, as “passive” devices. Although it is technically possible for these devices to contain their own internal sources of power, these power sources are prohibitively expensive at the present time. As used herein, however, the terms “smart card” and “smart inlay” are intended to include both passive devices and internally powered devices. The terms “smart card” and “smart inlay” also are intended to include both disposable (e.g., single use) and reuseable and/or reprogrammable RFID devices. Contactless and dual-interface smart cards and smart inlay devices all may be collectively referred to as “flexible transponders” in that they are small electronic circuits attached to or contained within a flexible physical carrier (such as plastic) and capable of receiving, transmitting, and storing data over RF waves (for example, by amplitude or frequency modulation) in a frequency range of approximately 100 kHz and 2.54 Ghz, depending on system design.
Because of the increasing recognition of possible fields of use, smart cards and smart inlays are being produced in ever increasing quantities. It is estimated that approximately two billion smart cards were produced world-wide during the year 2000 and some forecasts predict nearly six billion in the year 2003. Typically, the issuance of smart cards or smart inlays devices is an added business cost for the issuer not directly covered by the user. For example, issuance of smart cards for use on public transit facilities is usually not offset by higher fares to the users of those cards compared to other transit users. While the use of smart cards might encourage additional ridership and provide additional revenue, the issuance of cards is an added cost to the carrier. For this reason and others discussed herein, there is a significant need to find new ways to produce these increasing quantities of smart cards and smart inlays efficiently and cost effectively with improved manufacturing techniques.
Even with the advantages smart cards and smart inlays offer, product reliability is essential to marketplace acceptance and use. Dysfunctional smart cards and smart inlays result in considerable annoyance and dissatisfaction—both for consumers who rely on them and card/label issuers—and deter expansion of the “smart” technology into additional applications. Most smart cards and smart inlays are dynamically flexed, i.e., they are subject to flexion, in normal use. Although there are other applications, e.g., personal computers and automobiles, where computer circuits are flexed on a single occasion, i.e., during installation, they are not subjected to repeated flexing in normal use. Thus, the chips, antenna, and any other circuits and electronic components in smart cards and smart inlays are subjected to mechanical stresses not encountered by typical computer circuitry including these prior art “flex circuits.” Similarly, prior art RFID cards were designed to be hard and rigid to prevent flexion and thereby damage to the chip and circuit when used. As yet there has been no successful precedent to assist manufacturers in the production of massive quantities smart cards or smart inlays that are highly reliable. Thus, there is a great need to provide a system and methodology for forming inexpensive and reliable connections in smart cards and smart inlays in a high production environment.
Flexion of smart cards and smart inlays subject the chips and other miniaturized electronic components and circuits contained in them to considerable physical stress even with normal handling. Those forces can result in loss of electrical contact between components and inoperability of the smart card or smart inlay. The connection between a chip module and antenna in a contactless smart card or chip to antenna in a smart inlay is particularly vulnerable in normal use. Accordingly, any improved method for manufacturing smart cards and smart inlays must provide connectivity between electrical components that can withstand the physical abuse inherent with those products. However, current technologies for the connecting a chip or chip module to a substrate or antenna structure are still wasteful and painfully slow.
For example, in order to electrically connect a chip to a module at the contact areas of the module there exist two major techniques: wire bonding and flip-chip die bonding. Wire bonding is a process where a very thin metal wire is used to connect the chip bond pads to the contact lands on the module. A representative prior art process for fabricating a smart card using wire bonding of the chip module is shown in prior art FIGS. 1A-1E. Chip 100 is generally composed of silicon die 102 with multiple bond pads 104 as shown in prior art FIG. 1A. Chip 100 contains the necessary programming and data appropriate for the purpose of controlling the smart card. A chip carrier 105 for receiving chip 100 is shown in prior art FIG. 1B. Chip carrier 105 is composed of a distribution layer of contact lands 112 and conductive tracks (not shown), usually of copper; a substrate 106, generally of a glass epoxy; and contact plates 108, for example, of copper plated with nickel and gold, on the opposite side of substrate 106 from contact lands 112. The substrate 106 is formed with vias 110, or passages from one side of the substrate 106 to the other. These vias 110 are lined with the conductive walls 113 that extend through the vias 110 to make electrical contact with contact plates 108 on the opposite side of substrate 106.
The chip 100 is attached to the chip carrier 105 electrically by wire bonds 114 the form a chip module 115 as shown in prior art FIG. 1C. Typically a bonder will automatically bond one end of a wire to a bond pad 104 on the silicon die 102 and bond the opposite end of the wire either to contact lands 112 or through a via in the chip carrier substrate 106 (as shown) to form connection between the chip 100 and the contact plates 108 on the opposite side of the chip carrier 105. The electrical connections between the wire bond 114 and the chip 100 and the chip carrier 105, respectively, are formed through ultrasonic or thermal-sonic welding. A major disadvantage of this process is that each chip 100 needs to be connected through multiple wire bonds 114 with the chip carrier 105. This makes the chip attach process to the chip carrier 105 very time consuming and costly. Another disadvantage is that wire bonding also consumes up to 10 times the area of the chip 100, thus limiting the ability of this connection method to keep pace with the demand for miniaturization. Thermal-sonic welding of the wire bonds 114 creates high temperatures necessitating the selection of a chip carrier substrate 106 that can withstand such temperatures.
In order to mechanically connect the chip 100 to the chip carrier 105, the chip is generally glued to the substrate using a chip-attach adhesive (not shown). The chip 100 and the wire bonds 114 are then coated with an encapsulant 116. The encapsulant 116 further secures the chip 100 to the chip carrier 105 and protects the wire bonds 114 from mechanical and environmental damage. Encapsulant coating is another time consuming step in the module 115 assembly process, as the encapsulant 116 must cure before the module 115 can be handled further.
A dual-interface smart card blank 125 as shown in prior art FIG. 1D is composed of the card body 118 with a cavity 120 for receiving the chip module 115. The cavity 120 is further formed with a shelf 122 for supporting the edges of the chip module 115. The card body 118 further envelops antenna windings 128 that reside beneath the surface of the card body 118. The antenna 128 normally consists of several concentric loops or windings (depicted in the side view of FIG. 1, and as element 1228 in FIG. 12b) to provide adequate reception and transmission capability. The antenna 128 and card body 118 are typically prepared on a base by silver-paste printing and laminating. For example, the antenna 128 can be prepared by a silver-paste screen printing process with a cylinder screen-printing machine on an inner-layer sheet, typically PVC or similar material. Although not depicted in the drawing, the PVC and antenna can then be laminated together with graphically designed core-sheets and overlay-sheets with a thermo-transfer press.
Normally the card blank 125 with antenna 128 is manufactured in multi-card sheets. After lamination, the sheets are punched into single cards and then the cavity 120 for the chip module 115 is milled. Additional antenna cavities 123 extend below the shelf 122 to provide access to antenna contacts 128a and 128b for electrical connection to the chip module 115. The antenna cavities 123 are prepared by using special drilling tools to expose the antenna contacts 128a and 128b, as the depth has to be adjusted very carefully and precisely to reach the printed silver-paste track-ends. This type of antenna 128 is typically used for the 13.56 MHz Mifare system (available from Philips Semiconductors, Eindhoven, The Netherlands). The coil consists of 4 to 5 “windings,” with a total resistance after lamination of about 2 to 6 ohms.
FIG. 1D further shows the typical prior art preparation of a smart card body 118 for receipt of and electrical and mechanical connection with the chip module 115. Conductive adhesive 126 is dispensed in the antenna cavities 123 to provide the necessary electrical contact between the antenna contacts 128a and 128b and the contact lands 112 on the chip module 115. The conductive adhesive 126 connecting the contact lands 112 to the antenna contacts 128a and 128b may be a silver filled epoxy paste (e.g., EPO-TEK E4110 from Epoxy Technology Corp., represented by POLYTEC GmbH, D-76337 Waldbronn, Polytec-Platz 1-7). The chip 100 is thereby electrically connected both to antenna 128, which permits RF communication with an external device, and to contact plates 108 by way of the distribution tracks 113 in vias 110 that connect the contact lands 112 to the contact plates 108, which permits a physical electronic interface between the chip 100 and a card reader through the contact plates 108. In either case, the power for the chip 100 is supplied by the card reader or external RF device.
Additionally, nonconductive adhesive 124 is applied to the shelf 122 within the cavity 120 in order to mechanically secure the chip module 115 to the smart card body 118. The separate nonconductive adhesive 124 is used to hold the chip module 115 within the card body as it is less expensive and has better adhesive qualities than conductive adhesive 126. Using non-conductive adhesive 124 also prevents unwanted electrical connections across contact lands 112. However, care must also be taken in applying the non-conductive adhesive so that it does not cover or interfere with the electrical contact between the contact lands 112 and the antenna contacts 128a and 128b. 
Cyanoacrylate liquid adhesives are generally used as the nonconductive adhesive 124 in less expensive smart cards; in more critical smart card applications a double-sided, heat-curable, adhesive tape (e.g., TESA 8410 from Beiersdorf AG located at D-20245 Hamburg, Unnastrasse 48) is usually used. Normally this double-sided, heat-curable, non-conductive adhesive is first applied to the inner side of the chip module 115 with a hot-press. Then the chip module 115 is inserted into the cavity 120 and bonded to the card body 118 with the applied non-conductive adhesive 124 by heat and pressure. For the best adhesion and lifetime of this assembly, the cavity 120 should be treated before bonding the chip module 115 by a plasma (e.g., Plasma-System 4003 from Technics Plasma GmbH located at D-85551 Kirchheim bei München, Dieselstrsse 22a). Such a plasma treatment leads to very clean surfaces with a certain roughness and, therefore, allows a very durable bonding of the chip module 115 into the cavity 120 of the card body 118. A fully assembled prior art dual-interface smart card 130 is depicted in FIG. 1E.
In addition to the problems with wire bonds 114, the assembly of prior art smart cards using conductive adhesives results in even more disadvantages. The electrical characteristics of conductive adhesives change over a periods of seconds, minutes, and hours during curing. In practice this means that the completed smart cards cannot be tested immediately after assembly. With production rates measured in thousands of units per hour, any delay in testing can result in substantial yield losses in defective cards before a defect in the manufacturing process is detected. Productivity is also adversely impacted because cards must be stockpiled before testing can be completed. Accordingly, it is highly desirable to develop manufacturing processes in which the cards and labels can be tested immediately.
Among the other current chip bonding technologies used in RFID manufacturing, the most common chip-to-antenna connection processes include either flip-chip to chip carrier soldering, or flip-chip bonding with an anisotropic conductive adhesive of the chip to the chip carrier, and then a chip module to antenna connection utilizing conductive adhesive. For chip attachment, the most widely used process is traditional soldering technology, as modified for direct chip mounting. Often eutectic Pb/Sn solders for the bumping and connection process such as Pb/Sn 37/63 are used. Although it is widely used, the disadvantages are great. Due to relatively high temperatures of the soldering process, the selection of the substrate materials is limited to extremely high grade, high cost materials—not exactly a favorable condition for mass quantity, and in some cases disposable, mobile electronics products, especially paper or polypropylene substrates desired for smart inlays. In addition, recent changes in legislation addressing environmental and health concerns in the European Union, Japan, and the U.S. prescribe the use of lead-free soldering materials, which usually require a considerably higher processing temperatures or more expensive solders. Also, the preparation of a solderable metalization surface on the substrate before soldering, and a cleaning step after bonding, are necessary, which undoubtedly increase the complexity and the cost of the process. There is often additionally the requirement of underfilling the chip in this process, which is an added, time-consuming and cost incrementing step.
Flip chip bonding with anisotropic conductive adhesives (ACA) is another chip to chip carrier bonding method which is gaining more attention recently. ACAs can provide electrical as well as mechanical interconnections between chips and chip carriers, as well as modules to antenna coil pads. The conductivity of the ACA is restricted to the Z-direction while maintaining electrical isolation within the X-Y plane. In addition, the ACA materials act as an encapsulant and seal the underface of the flip. This eliminates the need for an additional underfill step. However, ACA is often up to 10 times more expensive than nonconductive adhesive. Further, surfaces often require chemical treatment before the ACA is applied in order to achieve adequate bond strength. Moreover, the mating surfaces, i.e., the chip bond pad, the antenna contact, and chip carrier contact land, have to be deoxided. The placement of the chip must be very accurate and only very limited tolerance is acceptable. Other disadvantages are high pressure requirements during the pick and place process, which can damage the chip, especially the thin chips used in smart cards and particularly smart inlays, and a highly sophisticated placement process for the expensive ACA materials (tape or film).
Flip-chip bonding with isotropic conductive adhesive is another influential chip bonding technique. The process generally lends itself well to integration into a production line. Yet there are clear limits with respect to cost, especially for small components and pitch distances since the electrical connection is provided by isotropically conductive adhesive, i.e., it will conduct in any direction and therefore must be placed discretely at individual bond sites. The high precision requirements therefore, significantly increase the cost of this technology. In this process, bumps are also added to the bond pads of the chips. These are generally nickel/gold bumps or stud bumps. In addition, high temperatures and a long curing process are usually required. Another notable disadvantage of either chip bonding technique using conductive adhesives, either isotropic or anisotropic, is that immediate testability is often impossible because of the long curing time required.
As a result of these factors, standard dual-interface smart cards and other RFID devices are currently manufactured using a combination of non-conductive adhesive (for holding parts together generally) and conductive adhesives (for forming an electrical connection at the contact lands or bond pads). Nevertheless, this compromise does not avoid the disadvantages previously noted. Accordingly, there is a significant need for improved manufacturing processes that can attach the components of smart cards and smart inlays, both cheaply and effectively.